This application claims the priority of German application 199 01 148.6, filed in Germany on Jan. 14, 1999, and German application 199 23 396.9 filed in Germany on May 21, 1999, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an apparatus for pneumatic condensing of a drafted fiber strand in a condensing zone arranged downstream of a front roller pair of a drafting apparatus, which condensing zone is limited in transport direction of the fiber strand by the nipping line of a delivery roller pair, said nipping line forming a twist block, and said delivery roller pair comprising a perforated suction roller, in whose inside a suction slit is arranged which extends essentially in transport direction to the nipping line.
An apparatus of this type is prior art in German published patent application 41 39 067. In the case of this apparatus, an apron pair is arranged around the front roller pair of the drafting apparatus, which apron pair guides the fiber strand exiting from the front roller pair into the condensing zone. The bottom apron of this apron pair is also guided over the bottom roller of the delivery roller pair. The upper roller of the delivery roller pair has suction openings and is thus in the form of a suction roller. The suction roller is not surrounded by the upper apron of the apron pair.
This apron pair, which loops the front roller pair of the drafting apparatus, requires, for a faultless drafting clamping of the fiber strand at the drafting apparatus, high pressures, which are higher than pressures in standard drafting apparatuses and which pressures diminish the life duration of the apron pair. In the zone where the fiber strand is double-guided by the apron pair, no condensing as yet takes place, as this can occur at the earliest at the suction roller. Because the bottom apron of the apron pair loops the bottom roller of the front roller pair as well as the bottom roller of the delivery pair, no differing peripheral speeds for an eventual tension draft between the front roller pair and the delivery roller pair can be set.
It is known from U.S. Pat. No. 4,488,397 that downstream of the actual drafting apparatus a condensing element in the form of a suction roller is arranged. This suction roller comprises, however, for the drafted fiber strand, a peripheral groove, so that no nipping point, which would clamp the fiber strand, can be formed with the suction roller. The twist block should rather more be effected in that the fiber strand loops the suction roller at a certain angle, so that the spinning twist, retroactive back to the drafting apparatus, is increasingly lost. In the area of the looping, the perforation of the suction roller is not suctioned, so that in this area also no pneumatic condensing takes place. Rather, the condensing takes place mechanically by means of the V-shaped ring groove.
It is an object of the present invention to utilize the entire distance between the front roller pair of the drafting apparatus and the delivery roller pair for the condensing of the fiber strand, and to create the possibility of setting a tension draft.
This object has been achieved in accordance with the present invention in that the suction roller is disposed directly downstream of the front roller pair and in that the fiber strand loops the suction roller up to the nipping line at an angle of at least 45.degree..
As there is no apron pair present in the condensing zone, the condensing effect can begin directly downstream of the drafting apparatus. As a result of the relatively large looping of the suction roller, the condensing zone is sufficiently long. In addition, it is possible to drive the front roller pair and the delivery roller pair at different peripheral speeds.
It has been shown that it is favorable for the condensing effect when a drafting plane, defined by the drafting apparatus, at least approximates a tangential plane guiding the fiber strand to the suction roller. The fiber strand is thus not deflected on its way from the front roller pair of the drafting apparatus to the suction roller.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.